In the past, since the main body of a BTE (Behind-The-Ear) hearing aid was exposed to the outside, the penetration of moisture, such as rain or perspiration, was a problem.
This was a particular problem with the battery case, and because it had a structure that was opened and closed during battery replacement, there was a gap between the hearing aid main body case and the battery case, making it extremely likely that water or perspiration would penetrate into the interior of the hearing aid.
In view of this, a hearing aid has been disclosed in the past in which the battery case is rotatably fitted to the hearing aid main body case, and a gasket is installed at the grounding face between the battery case opening and the opening at the lower end of the hearing aid main body case (see Patent Literature 1, for example). Consequently, the gasket is pressed when the battery case is closed, and this prevents the penetration of rain or perspiration into the battery case.
Also, there has been a disclosure in which the entire battery case is housed inside the hearing aid main body case, a groove is formed in the inner wall face of the battery case, and a hole is provided in the lower part of this groove, which allows any moisture that does penetrate to drain away (see Patent Literature 2, for example).